1. Field of the Invention
The present invention relates to an ink jet recorder in which the ink jet head is restored to its initial condition with a cap covering the ink ejection orifices of the head at a predetermined restoring position, and with a suction device sucking the residual ink in the head through the cap covering the orifices. In particular, the invention relates to an ink jet recorder in which it is possible to restore the ink jet head by sucking with a simple control mechanism the residual ink in the head, while maintaining the capping performance for the head over a long period of time by preventing degradation, permanent deformation, etc. of the cap even if the gap between the head and the cap varies with factors such as the irregularity in thickness of sheets of printing paper and the irregularity in dimensional precision of the cap and peripheral mechanisms.
2. Description of the Related Art
In a conventional ink jet recorder including an ink jet head, from which ink can be ejected onto a recording medium so as to record characters etc., it is possible to restore the head by covering the head with a cap at a predetermined restoring position, and then sucking and removing the residual ink in the head through the suction device communicating with the cap.
Japanese Patent Laid-Open Publication No. 6-126947, for example, discloses an ink jet recorder including an ink jet type recording head mounted on a carriage. Placed at the home position of the carriage is a capping unit including a cap for sealing the ink ejection orifices of the recording head. The capping unit is connected through a tube to a pumping unit. When the recording head cannot eject ink, the pumping unit is actuated to develop negative pressure in the cap for sucking ink through the ejection orifices of the recording head so as to restore the head.
If the cap of the capping unit was separated from the recording head immediately after the suction, atmospheric pressure would be applied instantaneously to the interior of the cap, in which negative pressure remains. This would cause a rapid change of pressure, which might break or destroy the menisci in the ink ejection orifices. As a result, air might be entrained into the orifices, causing defective ejection of ink. Furthermore, when the cap is separated, the residual ink in the cap might spill outside.
In order for these problems to be solved, in the ink jet recorder of the publication No. 6-126947, the carriage is first moved slightly when the ink ejection orifices of the recording head are sealed with the cap after the suction. This may form a slight gap between the recording head and the cap. Then, the pumping unit is actuated to suck ink and air. A gap is not necessarily formed between the head and the cap due to the irregularity in the cap size.
In some ink jet recorders, the recording head is positioned in accordance with the thickness of the recording medium so that the gap between the recording surface of the medium and the head is constant. Thus, the positioning of the recording head changes the gap between the head and the cap. In such cases also, a slight gap is not necessarily formed between the head and the cap.
Therefore, in the ink jet recorder of the publication No. 6-126947, the pumping unit is actuated to suck ink with the carriage moved slightly. Thereafter, the carriage is further moved slightly to a position where a gap is formed between the recording head and the cap. At the same time, ink is sucked through the pumping unit. Consequently, even if the dimensional precision etc. of the cap and peripheral mechanisms are irregular, air is prevented from being entrained into the ejection orifices by virtue of the gap formed between the head and cap. In addition, the ink in the cap can be sucked effectively so that it is possible to minimize the amount of ink remaining on or at the ink ejection surface of the recording head.
In the ink jet recorder disclosed in the publication No. 6-126947, slight movement of the carriage forms a gap between the recording head and the cap. As apparent from the drawings accompanying the publication, the slight movement of the carriage deforms the cap, which is made of rubber or the like, so as to form the gap between the head and the cap. Accordingly, the cap is deformed every time the recording head is restored. This may degrade and/or permanently deform the cap. If the cap degrades and/or permanently deforms, it is not possible to restore the recording head effectively.
Generally, in an ink jet recorder the recording head of which can be restored by suction, it is easier to control the printing and the restoration by suction independently or separately than together. Furthermore, in many cases, the independent controlling easily makes the controlling speed high.
In the ink jet recorder of the publication No. 6-126947, it is necessary to move the carriage slightly when the recording head is sucked for restoration. It is therefore necessary to control the carriage movement in addition to the restoration by suction. In such a case, it is difficult to control the restoration by suction simply, and to speed up the controlling.